Level of physical activity is a determinant of morbidity and mortality for many health problems. Although there are health benefits from sustained physical activity, there is widespread physical inactivity in the US population. Children and adolescents are more physically active than adults; however, many do not reach recommended levels of physical activity. Girls spend less time in physical activity than boys, and adolescents are less active than younger children. The decrease in physical activity among girls is particularly evident by middle school (6th to 8th grades). Girls report barriers to physical activity such as embarrassment because of lack of skills, unwillingness to "dress out", emphasis on team sports, lack of transportation, and safety issues. There have been few physical activity intervention programs for girls in this age group; hence there is an important need to develop and test the effectiveness of a coordinated school-based physical activity intervention with linkages to community agencies. The Trial of Activity for Adolescent Girls (TAAG) is a multi-site, multi-component program to increase the number of minutes of moderate to vigorous activity both during and after school and to improve cardiorespiratory fitness. This will be accomplished by developing a TAAG physical education program, a TAAG health education course, and a TAAG after school physical activity program in collaboration with community partners. Six middle schools and their catchment areas will be identified in the New Orleans area. Schools will be paired based on ethnicity and socioeconomic status, and after baseline measurements (Spring 2003) on sixth-grade girls, one school in each pair will be randomized to receive all interventions and measurements while the other school receives measurements only. Measurements will be repeated annually, including the end of the intervention (Spring 2005) and after one year of follow-up (Spring 2006). TAAG has the potential to provide a sustainable program that can be disseminated to middle schools throughout the country in order to increase physical activity for girls.